Conductive Patterns and Methods of Using Them

ABSTRACT

Conductive patterns and methods of using and printing such conductive patterns are disclosed. In certain examples, the conductive patterns may be produced by disposing a conductive material between supports on a substrate. The supports may be removed to provide conductive patterns having a desired length and/or geometry.

PRIORITY APPLICATIONS

This application claims priority to U.S. Provisional Application No.60/826,605 filed on Sep. 22, 2006 and to U.S. Provisional ApplicationNo. 60/866,750 filed on Nov. 21, 2006, the entire disclosure of each ofwhich is hereby incorporated herein by reference for all purposes.

FIELD OF THE TECHNOLOGY

Embodiments of the technology disclosed herein relate generally toconductive patterns and methods of using and printing them. Moreparticularly, certain embodiments relate to electronic devices, such asprinted circuit boards, that include one or more conductive patterns asdisclosed herein.

BACKGROUND

Electronic devices include numerous connected electrical circuits. Asthe footprint of devices becomes smaller, the circuitry of the devicesmust be reduced to accommodate a desired footprint. Current methods usedto produce circuits and conductors do not provide the precision tocreate narrow and thin conductors for use in many small electronicdevices.

SUMMARY

In accordance with a first aspect, a device comprising at least oneconductive pattern is disclosed. In certain embodiments, the conductivepattern may take the form of one or more conductive lines which may beelectrically coupled to one or more other conductive lines. In certainexamples, the conductive pattern may be produced by disposing a supporton a substrate, disposing a conductive material between the support, andremoving the support. Conductive patterns produced using such a methodare referred to in some-instances herein as high-aspect ratio conductivepatterns. In some examples the conductive material may be a metalparticles, such as the capped metal particles described herein.

In accordance with an additional aspect, a substrate comprising at leastone high-aspect ratio conductive pattern is provided. In certainexamples, the substrate may be part of a printed circuit board. In someexamples, the substrate may be formed from one or more pre-pregs thathave been thermally treated. In other examples, the substrate may takethe form of a laminate or a molded article. In certain embodiments, theconductive pattern may include one or more conductive lines which may beelectrically coupled to one or more other conductive lines. Theconductive pattern may be disposed horizontally along the plane of thesubstrate, vertically and substantially perpendicular to the plane ofthe substrate or at any angle to the plane of the substrate. In certainconfiguration a first high-aspect ratio conductive pattern may beelectrically coupled to another conductor, which may be a high-aspectratio conductive pattern, on an opposite or other face of the substrate.

In accordance with another aspect, a printed circuit board comprising atleast one high aspect ratio conductive line is provided. In certainexamples, the printed circuit board may be formed from one or moreprepregs that include at least one high-aspect ratio conductive patterndisposed on one of the prepregs.

In accordance with another aspect, a method of producing a high-aspectratio conductive pattern is disclosed. In certain examples, the methodincludes disposing a conductive material between a solid support. Incertain examples, the solid support may include a defined spacing toprovide a conductive pattern with a desired geometry, thickness orwidth. The method may also include removing the solid support to providea high-aspect ratio conductive pattern. In certain examples, the solidsupport may be removed by thermal treatment, chemical treatment or othermethods that may remove the solid support without damage to theconductive pattern. In certain examples, the solid support may include aanti-wetting coating to prevent or reduce the tendency of the ink tospread.

In accordance with another aspect, a method of producing a printedcircuit board comprising at least one high-aspect ratio conductivepattern is provided. In certain examples, the method includes disposinga conductive material between a solid support on a prepreg, and removingthe solid support from the prepreg to provide a high-aspect ratioconductive pattern. The method may also include thermally treating theprepreg with the at least one disposed high-aspect ratio conductivepattern to provide a printed circuit board.

In accordance with an additional aspect, a method of facilitatingassembly of an electronic device is disclosed. In certain examples, themethod comprises providing at least one ink comprising capped metalparticles, and providing instructions for disposal of the at least oneink on a substrate to provide a high-aspect ratio conductive pattern onthe substrate.

In accordance with another aspect, a method of printing a conductorusing a printer is provided. In certain examples, the method comprisesdisposing a solid support material in a first reservoir of the printeron a substrate. In some examples, the method further comprises disposingan ink in a second reservoir of the printer between the disposed solidsupport material on the substrate. In certain examples, the method mayalso include removing the disposed solid support material from thesubstrate.

Additional features, aspects and examples are described in more detailbelow.

BRIEF DESCRIPTION OF THE FIGURES

Certain embodiments are described below with reference to theaccompanying figures in which:

FIG. 1 is a drawing of solid supports disposed on a substrate, inaccordance with certain examples;

FIG. 2 is a drawing of a conductive material disposed between solidsupports on a substrate, in accordance with certain examples;

FIG. 3 is a drawing of a high-aspect ratio conductive pattern disposedon a substrate, in accordance with certain examples;

FIG. 4 shows a method for producing a high-aspect ratio conductivepattern, in accordance with certain examples; and

FIG. 5 is an example of a printed circuit board including a high-aspectratio conductive pattern, in accordance with certain examples.

Certain features shown in the figures may have been enlarged, distorted,altered or otherwise shown in non-conventional manner to facilitate abetter understanding of the technology disclosed herein.

DETAILED DESCRIPTION

Certain embodiments of the devices and methods disclosed herein provideelectrically conducting patterns having electrical properties notpreviously achieved with existing methods. High-aspect ratio conductivepatterns may be produced on any type of electrical device in any desiredpattern of selected thicknesses and widths. Illustrative high-aspectratio conductive patterns are disclosed below.

Piezoelectric inkjet technology has advanced to become a key enabler inprinted electronics. As an additive process, inkjet printing preciselycontrols the order and amount of fluids applied so expensive fluids andmaterials are not wasted. As an extended range of jettable nanoparticleconductive, semi-conductive, and adhesive fluids become commerciallyavailable, new opportunities for inkjet are emerging in the electronicindustry.

Piezoelectric inkjet technology has advanced to become a key enabler inprinted electronics. As an additive process, inkjet printing preciselycontrols the order and amount of fluids applied so expensive fluids andmaterials are not wasted. As an extended range of jettable nanoparticleconductive, semi-conductive, and adhesive fluids become commerciallyavailable, new opportunities for inkjet are emerging in the electronicindustry.

One drawback in inkjet technology is printing of narrow (less than about100 microns wide) and thick lines (more than about 2 microns thick).Normally to achieve required line thickness multiple printing passes areneeded which could result in spreading the line beyond the requiredwidth. The phenomenon can be especially severe in the case of conductingmetallic inks. Metal particles are much denser then the carrier mediatherefore most of the ink volume is taken by solvents which readilyspread on the printed surface.

To prevent the ink spread common practice is the addition of rheologymodifiers to increase the viscosity and tackiness of the ink. However,the addition of rheology modifiers (usually high boiling organicmaterials and polymers) to the conductive ink formulation may result ina significant degradation of the conductivity of the printed lines. Thisis especially true in the case of the metallic nanoparticle inks, suchas those described in U.S. application Ser. No. 11/462,089, the entiredisclosure of which is hereby incorporated herein by reference for allpurposes. The sintering of nanoparticles into highly conductive linesrelies on the intimate contact between the nanoparticles so addition ofhigh boiling organic materials and polymers can impede or completelyblock the sintering process resulting in poor quality lines.

In accordance with certain examples, a method that provides for ink jetprinting of fine patterns of any dimensions with inks of any viscosityto provide a high-aspect ratio conductive pattern is disclosed. The term“high-aspect ratio” refers to the electrical conductor as having a firstdimension, e.g., a height, that is at least about five times greaterthan a second dimension, e.g., a width. In certain examples, the firstdimension is at least about 10, 20, 30, 40, 50, 60, 70, 80, 90 or 100times greater than the second dimension. The method used herein,however, may also be used to print conductive patterns having heightsand widths that are substantially the same, e.g., 1:1 ratio ofheight:width or conductive patterns where the height is about twice thatof the width, e.g., 2:1 ratio of height:width.

In accordance with certain embodiments, the conductive material may bedisposed between two or more supports. For example and referring to FIG.1, a side-view of a substrate 100 is shown. A first solid support 110and a second solid support 120 have been disposed on the substrate 100.Though solid supports 110 and 120 are shown as being disposed near thecenter of the substrate 100, the solid supports 110 and 120 may bedisposed at any portion or area of the substrate 100. Subsequent todisposal of the solid support 110 and 120 on the substrate 110, aconductive material 130 may be disposed between the solid support 110and 120, as shown in FIG. 2. The height h₁ of the solid supports and thedistance d₁ between the solid supports generally determines thethickness and width of the conductive material, respectively. Bydecreasing the distance d₁, the width of the conductive pattern willdecrease. By decreasing the height h₁, the thickness of the conductivepattern will decrease. The actual thickness and width of the conductivepattern may vary and illustrative thicknesses range from about 0.001 mmto about 0.1 mm and illustrative widths include, but are not limited to,0.05 mm to about 0.3 mm. Additional thicknesses and widths will bereadily selected by the person of ordinary skill in the art, given thebenefit of this disclosure.

In accordance with certain examples, once the conductive material 130 isdisposed between the solid supports 110 and 120, the conductive materialmay be subjected to one or more treatment steps. In examples where theconductive material is a an ink comprising capped metal particles, suchas the ones described below, the ink may be sintered to condense thedisposed material Other treatment steps include, but are not limited to,heating, grinding, chemical etching, and plasma etching. Additionaltreatment steps to provide high-aspect ratio conductive patterns will bereadily selected by the person of ordinary skill in the art, given thebenefit of this disclosure.

In accordance with certain examples, various methods may be used todispose the solid supports onto a substrate. The exact method used todispose the solid support material onto a substrate may vary dependingon the nature and properties of the material selected for use in thesolid support. In examples where the solid support is a polymericmaterial, the solid support may be disposed by inkjet printing, screenprinting, or gravure printing. In examples where the solid support is apaper based material, an inorganic salt or an elastomer such as rubber,the solid support may be disposed or packed in a mold or form placedover the substrate. Other suitable materials for use in the solidsupport include, but are not limited to polymers, epoxy resins,inorganic/organic salts. In some examples when the solid support alsoprovides anti-wetting properties it can be made of fluorinated polymers,such as Krytox fluids from Dupont or FluoroPel from Cytonix corporation.In some examples, the solid support may be disposed using an inkjetprinter, such as an inkjet printer that may be used to dispose theconductive material. For example, the inkjet printer may include two ormore reservoirs, one including the solid support material and the otherincluding the ink to be printed between the solid supports. A firstprinting of the substrate may dispose the solid support material, and asecond printing of the substrate may dispose the conductive materialbetween the solid support material. Computer control of the printingoperation may provide for known and precise disposal of both the solidsupport material and the ink.

In accordance with certain examples, subsequent to disposal of the solidsupport material and the ink, the solid support material may be removedto provide a high-aspect ratio conductive pattern. In certain examples,the solid supports 110 and 120 may be removed from the substrate 100 toprovide a high-aspect ratio conductive pattern 140, as shown in FIG. 3.The exact method or process used to remove the solid supports depends onthe nature of the material or materials used in the solid supports. Inexamples where the solid support is a polymer, such as a plastic, thepolymer may be stripped by washing it with organic solvents such asisopropyl alcohol or acetone or commercial strippers available forstripping photoresist films. In certain examples, the solid supports maybe grinded or cut away with a CNC machine or other device that mayremove the solid supports without substantial damage to the disposedconductive material. In examples where the solid support is paper, thesolid supports may be burned or ashed and an air stream may be used toremove the residue from the conductive material. In certain examples,the solid support may be cast using an inorganic material, and, afterdisposition of the conductive material, the inorganic material may bedissolved away with a mild acid or base depending on the nature of theinorganic material. Illustrative inorganic materials include, but arenot limited to, sodium chloride, potassium chloride, sodium nitrate andother water soluble salts.

In certain examples, the conductive material may be disposed step-wise,followed by subsequent disposal of more solid support material andsubsequent disposal of additional conductive material. This process maybe useful, for example, where it is desirable to achieve a conductivematerial thickness greater than is capable with a single application. Anillustration of this process is shown schematically in FIG. 4. Asubstrate 400 is shown in FIG. 4, and a polymeric solid support materialalong with a conductive nanosilver ink is shown as being used. In afirst step, supporting polymer line 410 and 415 are printed on thesubstrate 400. A silver ink 425 is printed between solid support lines410 and 415 until it reaches the top of solid support lines 410 and 415.Additional solid support material is disposed on lines 410 and 415 toprovide solid support lines 430 and 435. Additional ink 445 is disposedbetween solid support lines 430 and 435 until the ink reaches the top ofthe solid support lines 430 and 435. Another step of disposingadditional solid support material to provide solid support lines 450 and455 followed by disposal of additional ink 465 may also be performed.This process of disposing solid support material followed by disposal ofink may be continued until a desired thickness is reached. Once adesired thickness is reached, sintering may be performed to condense theink 465 to a sintered ink 475. Subsequent to sintering, solid supportlines 450 and 455 may be removed by washing the substrate in, forexample, isopropyl alcohol, acetone or a mixture thereof to leave asubstrate 400 having a high-aspect ratio conductive pattern 485.

In accordance with certain examples, inks suitable for use in themethods disclosed herein include, but are not limited to, any inksuitable for use in inkjet printing applications. Illustrative inks andparticles for use in such inks are discussed below. Additional suitableinks will be readily selected by the person of ordinary skill in theart, given the benefit of this disclosure.

In accordance with certain examples, the ink may include silverparticles dispersed in a suitable solvent system. Silver particles arewell known materials and available from different commercial sources.Normally, the size of particles ranges from 5 to 70 nm. The knownadvantage of particles compared to regular silver powder is theirability to be heated or sintered in solid structures at temperaturesmuch lower then melting temperatures. The silver particles can beheated, for example, at temperatures as low as 200° C. The heatingprocess is a diffusion process in which silver migrates from particle toparticle forming connecting bridges between particles. The structuresformed by heating of currently available silver particles areconductive, but their conductivity is still much lower then that of bulksilver. The reported conductivity is in the range of 1-2*10⁴ S/cmcompared to 62*10⁴ S/cm for the bulk silver. There remains a need forsilver films whose conductivity is much closer to that of bulk silver.

In accordance with certain examples, particles suitable for use in theinks disclosed herein may be produced by mixing at least one metal ormetal salt and a capping agent in a single phase solution or in amulti-phase solution. In certain examples, the metal or metal salt maybe selected from conductive metals or conductive metal salts including,for example, transition metals or transition metal salts of gold,silver, copper, nickel, platinum, palladium, iron, and alloys thereof.The exact form of the metal or metal salt may vary depending on theselected solvent system. It is desirable that the metal salt dissolve inthe selected solvent system without undue heating that could result inevaporation of the solvent. Illustrative anions of the metal saltsinclude nitrate, chloride, bromide, iodide, thiocyanate, chlorate,nitrite, and acetate. Additional anions are disclosed below in referenceto the particular illustrative metal salts disclosed.

In certain examples, the use of a single phase solution to produce theparticles permits omission of a phase transfer reagent (though a phasetransfer reagent may still be used in certain embodiments) that iscommonly used to produce particles in a polyol process. By performingthe reaction in a single phase, the ease of producing the particlesincreases, and the cost of producing the particles decreases. Inaddition, large scale, industrial synthesis of the particles may beachieved using a single phase reaction. Additional benefits of theparticles, and methods of producing them, will be readily selected bythe person of ordinary skill in the art, given the benefit of thisdisclosure.

In accordance with certain examples, a silver salt may be used toprovide particle suitable for use in the inks disclosed herein. Ininstances where a silver salt is used, the silver salt may be one ormore of silver chloride, silver bromide, silver iodide, silverthiocyanate, silver sulfate, silver chromate, silver phosphate, silveroxalate, silver carbonate, silver sulfite, silver hydroxide, silvernitrate, silver chlorate, silver acetate, silver nitrite, silveracetylacetonate, silver lactate, silver (II) fluoride, silver (I)hydrogenfluoride, silver (I) permanganate, silver metavanadate, silvertrifluoroacetate, potassium dicyanoargentate, silver benzoate, silverarsenate, silver bromate, silver cyclohexanebutyrate, silverfluorosulfate, silver hexafluoroantimonate (V), silverhexafluoroarsenate (V), silver hexafluorophosphate, silver (I) fluoride,silver (I) oxide, silver (I) perrhenate, silver (I) selenide, silver (I)telluride, silver iodate, silver orthophosphate, silver sulfide, andsilver tungstate. Additional suitable silver salts will be readilyselected by the person of ordinary skill in the art, given the benefitof this disclosure.

In accordance with certain examples, a gold salt may be used to provideparticles suitable for use in the inks disclosed herein. In instanceswhere a gold salt is used, the gold salt may be one or more of gold(III) chloride hydrate, hydrogen tetrachloroaurate (III) hydrate,chloro(dimethylsulfide) gold (I), gold (I) chloride, gold colloid, gold(I) cyanide, gold (I) iodide, gold (I) sulfide, gold (III) bromidehydrate, gold (III) chloride, gold (III) chloride trihydrate, gold (III)hydroxide, gold (III) oxide hydrate, gold (III) sulfide, potassiumdicyanoaurate (I), potassium gold (III) chloride, and sodiumtetrachloroaurate (III) dehydrate. Additional suitable gold salts willbe readily selected by the person of ordinary skill in the art, giventhe benefit of this disclosure.

In accordance with certain examples, a copper salt may be used toproduce particles suitable for use in the inks disclosed herein. Ininstances where a copper salt is used, either the cuprous form (copper(I)) or the cupric form (copper (II)) may be used. Illustrative coppersalts include, but are not limited to, copper (I) chloride, copper (II)chloride, copper (I) bromide, copper (II) bromide, copper (I) iodide,copper (II) iodide, copper mercuric iodide, copper (I)tetraiodomercurate (II), cuprous thiocyanate, copper (II) sulfate,copper(II) acetylacetonate, ammonium tetrachlorocuprate (II) dihydrate,copper aluminum oxide, copper chromite, ethylenediaminetetraacetic aciddiammonium copper salt solution, ethylenediaminetetraacetic acid copper(III) disodium salt, copper (I) acetate, copper (I) cyanide, copper (I)oxide, copper (I) selenide, copper (I) sulfide, copper (I) telluride,copper (I) thiophenolate, copper (II) acetate, copper(II) acetatehydrate copper (II) acetate monohydrate, copper (II) carbonate, copper(II) hydroxide, copper (II) molybdate, copper (II) niobate, copper (II)nitrate, copper (II) selenide, copper (II) selenite dehydrate, copper(II) sulfate, copper (II) sulfide, copper (II) telluride,tris(ethylenediamine) copper (II) sulfate, and combinations thereof.Additional suitable copper salts will be readily selected by the personof ordinary skill in the art, given the benefit of this disclosure.

In accordance with certain examples, an aluminum salt may be used toprovide particles suitable for use in the inks disclosed herein. Ininstances where an aluminum salt is used, the aluminum salt may be, forexample, one or more of aluminum acetate, aluminum phosphate monobasic,aluminum sulfate, aluminum ethoxide, aluminum potassium sulfate,aluminum silicate, aluminum acetate, aluminum arsenide, aluminumbromide, aluminum chloride, aluminum chloride hydrate, aluminumfluoride, aluminum fluoride hydrate, aluminum fluoride trihydrate,aluminum hydroxide, aluminum iodide, aluminum sulfide, aluminum nitrate,aluminum thiocyanate, aluminum chlorate, and aluminum nitrite.Additional suitable aluminum salts will be readily selected by theperson of ordinary skill in the art, given the benefit of thisdisclosure.

In accordance with certain examples, a platinum salt may be used toproduce particles suitable for use in the inks provided herein. Ininstances where a platinum salt is used, the platinum salt may be, forexample, one or more of platinum (II) acetylacetonate, platinum (IV)chloride, platinum (IV) oxide, platinum (II) bromide, platinum (II)chloride, platinum (II) cyanide, platinum (II)hexafluoroacetylacetonate, platinum (II) iodide, platinum (IV) sulfide,and platinum nitrate. Additional suitable platinum salts will be readilyselected by the person of ordinary skill in the art, given the benefitof this disclosure.

In accordance with certain examples, a palladium salt may be used toproduce particles suitable for use in the inks disclosed herein. Ininstances where a palladium salt is used, the palladium salt may be, forexample, one or more of palladium (II) acetylacetonate, palladium(II)trifluoroacetate, palladium hydroxide, palladium (ID acetate,palladium(II) bromide, palladium (II) chloride, palladium(II) cyanide,palladium(II) hexafluoroacetylacetonate, palladium(II) iodide,palladium(II) nitrate dehydrate, palladium(II) nitrate hydrate,palladium(II) oxide, palladium (II) propionate, palladium (II) sulfate,palladium (II) sulfide, and palladium on alumina. Additional suitablepalladium salts will be readily selected by the person of ordinary skillin the art, given the benefit of this disclosure.

In accordance with certain examples, a cobalt salt may be used toproduce particles suitable for use in the inks disclosed herein. Ininstances where a cobalt salt is used, the cobalt salt may be, forexample, one or more of ammonium cobalt (II) sulfate hexahydrate, cobaltchloride, cobalt (II) acetate, cobalt (II) acetate tetrahydrate, cobalt(II) acetylacetonate, cobalt (II) acetylacetonate hydrate, cobalt (II)bromide, cobalt (ID chloride, cobalt (II) chloride hexahydrate, cobalt(II) chloride hydrate, cobalt (II) cyanide dehydrate, cobalt (II)iodide, cobalt (II) thiocyanate, cobalt (II) nitrate hexahydrate, andcobalt (III) acetylacetonate. Additional suitable cobalt salts will bereadily selected by the person of ordinary skill in the art, given thebenefit of this disclosure.

In accordance with certain examples, a chromium salt may be used toproduce particles suitable for use in the inks disclosed herein. Ininstances where a chromium salt is used, the chromium salt may be, forexample, one or more of chromium (III) acetylacetonate, chromium (II)acetate, chromium (ID chloride, chromium (II) fluoride, chromium (II)selenide, chromium (III) acetate hydroxide, chromium (III) bromidehexahydrate, chromium (III) chloride, chromium (III) chloridehexahydrate, chromium (III) chloride hydrate, chromium (III) fluoride,chromium (III) sulfate hydrate, chromium (III) telluride, chromiumsilicide, and chromium nitrate. Additional suitable chromium salts willbe readily selected by the person of ordinary skill in the art, giventhe benefit of this disclosure.

In accordance with certain examples, an indium salt may be used toproduce particles suitable for use in the inks disclosed herein. Ininstances where an indium salt is used, the indium salt may be, forexample, one or more of indium (III) acetylacetonate, indium antimonide,indium (I) bromide, indium (I) chloride, indium (I) iodide, indium (II)chloride, indium (III) acetate, indium (III) acetate hydrate, indium(III) bromide, indium (III) chloride, indium (III) chloride hydrate,indium (III) chloride tetrahydrate, indium (III) fluoride, indium (III)fluoride trihydrate, indium (III) hydroxide, indium (III) iodide, indium(III) nitrate hydrate, indium (III) nitrate hydrate, indium (III)nitrate pentahydrate, indium (III) nitride, indium (III) oxide, indium(III) perchlorate hydrate, indium (III) selenide, indium (III) sulfate,indium (III) sulfate hydrate, and indium (III) telluride. Additionalsuitable indium salts will be readily selected by the person of ordinaryskill in the art, given the benefit of this disclosure.

In accordance with certain examples, a nickel salt may be used toproduce particles suitable for use in the inks disclosed herein. Ininstances where a nickel salt is used, the nickel salt may be, forexample, one or more of nickel (II) acetylacetonate, nickel (II) acetatetetrahydrate, nickel (II) carbonate hydroxide tetrahydrate, nickel (II)octanoate hydrate, nickel sulfide, nickel carbonate, nickel (II)bromide, nickel (II) bromide hydrate, nickel (II) bromide trihydrate,nickel (II) carbonate basic hydrate, nickel (II) chloride, nickel (II)chloride hexahydrate, nickel (II) chloride hydrate, Nickel (II)cyclohexanebutyrate, nickel (II) fluoride, nickel (II) fluoridetetrahydrate, nickel (II) hexafluoroacetylacetonate hydrate, nickel (II)hydroxide, nickel (II) iodide, nickel (II) molybdate, nickel (II)nitrate hexahydrate, nickel (II) oxalate dehydrate, nickel (II) oxide,nickel (II) perchlorate hexahydrate, nickel (II) peroxide hydrate,nickel (II) phosphide, nickel (II) stearate, nickel (II) sulfatehexahydrate, and nickel on silica. Additional suitable nickel salts willbe readily selected by the person of ordinary skill in the art, giventhe benefit of this disclosure.

In accordance with certain examples, an iridium salt may be used toproduce particles suitable for use in the inks disclosed herein. Ininstances where an iridium salt is used, the iridium salt may be, forexample, one or more of iridium (III) acetylacetonate, iridium (III)bromide hydrate, iridium (III) chloride, iridium (III) chloride hydrate,iridium (III) chloride hydrochloride hydrate, iridium (IV) chloridehydrate, iridium (IV) oxide, iridium (IV) oxide hydrate and iridiumnitrate. Additional suitable iridium salts will be readily selected bythe person of ordinary skill in the art, given the benefit of thisdisclosure.

In accordance with certain examples, a rhodium salt may be used toproduce particles suitable for use in the inks disclosed herein. Ininstances where a rhodium salt is used, the rhodium salt may be, forexample, one or more of rhodium (III) acetylacetonate, rhodium (II)acetate dimmer, rhodium (II) acetate dimer dehydrate, rhodium (II)heptafluorobutyrate, rhodium (II) hexanoate, Rhodium (II) octanoatedimer, rhodium (II) trifluoroacetate dimer, rhodium (II)trimethylacetate dimer, rhodium (III) bromide hydrate, rhodium (III)chloride, rhodium (III) chloride hydrate, rhodium (III) iodide hydrate,rhodium (III) nitrate hydrate, rhodium (III) oxide, rhodium (III) oxidehydrate, rhodium (III) phosphate solution, sodium hexachlororhodate(III) dodecahydrate, rhodium (III) sulfate solution, rhodium (IV) oxide,rhodium on activated alumina, rhodium on activated charcoal,tris(ethylenediamine) rhodium (III) chloride, andtris(ethylenediamine)-rhodium (III) nitrate. Additional suitable rhodiumsalts will be readily selected by the person of ordinary skill in theart, given the benefit of this disclosure.

In accordance with certain examples, an osmium salt may be used toproduce particles suitable for use in the inks disclosed herein. Ininstances where an osmium salt is used, the osmium salt may be, forexample, one or more of osmium (III) chloride hydrate, osmiumtetrachloride, osmium tetroxide, osmium trichloride andtetra-osmium-nitrate. Additional suitable osmium salts will be readilyselected by the person of ordinary skill in the art, given the benefitof this disclosure.

In accordance with certain examples, an iron salt may be used to produceparticles suitable for use in the inks disclosed herein. In instanceswhere an iron salt is used, the iron salt may be, for example, one ormore of iron (III) acetylacetonate, iron (II) acetylacetonate, ironascorbate, ammonium iron (II) sulfate hexahydrate, iron (III) citratetribasic monohydrate, iron (II) gluconate dehydrate, iron (III)pyrophosphate, iron (II) phthalocyanine, iron (III) phthalocyaninechloride, ammonium iron (III) citrate, ammonium iron (II) sulfate,ammonium iron (III) sulfate, ammonium iron (III) sulfate dodecahydrate,iron (III) chloride, iron (III) bromide, iron (III) chloridehexahydrate, ferric citrate, iron (III) fluoride, iron (III) nitratenonahydrate, iron (III) oxide, iron (III) phosphate, iron (III) sulfatehydrate, iron (II) bromide, iron (II) chloride, iron (III) phosphatehydrate, iron (III) phosphate tetrahydrate, iron (II) chloride hydrate,iron (II) chloride tetrahydrate, iron (II) ethylenediammonium sulfatetetrahydrate, iron (II) fluoride, iron (II) gluconate hydrate, iron (II)iodide, iron (II) lactate hydrate, iron (II) oxalate dehydrate, ferroussulfate heptahydrate, iron (II) sulfide, iron (II) acetate, iron (II)fluoride tetrahydrate, iron (II) iodide tetrahydrate, iron (II)molybdate, iron (II) oxide, iron (II) perchlorate hydrate, iron (II)titanate, and iron (III) ferrocyanide. Additional suitable iron saltswill be readily selected by the person of ordinary skill in the art,given the benefit of this disclosure.

In accordance with certain examples, a ruthenium salt may be used toproduce particles suitable for use in the inks disclosed herein. Ininstances where a ruthenium salt is used, the ruthenium salt may be, forexample, one or more of ruthenium (III) acetylacetonate, ruthenium (IV)oxide, ammonium hexachlororuthenate (IV), ruthenium (III) chloride,ruthenium on activated charcoal, ruthenium on alumina, ruthenium oncarbon, ruthenium (III) bromide, ruthenium (III) chloride hydrate,ruthenium (III) chloride trihydrate, ruthenium (III) iodide, ruthenium(III) nitrosyl chloride hydrate, ruthenium (III) nitrosyl nitratesolution, and ruthenium (IV) oxide hydrate. Additional suitableruthenium salts will be readily selected by the person of ordinary skillin the art, given the benefit of this disclosure.

In accordance with certain examples, the metal used to provide theparticles for use in the inks disclosed herein may be uncomplexed or maybe complexed with one or more ligands. For example, the metal may becomplexed with EDTA, ethylenediamine, oxalate, 2,2′-bypyridine,cyclopentadiene, diethylenetriamine, 2,4,6,-trimethylphenyl,1,10-phenanthroline, triethylenetetramine or other ligands.

In accordance with certain examples, the inks disclosed herein mayinclude two or more different metal particles suspended in a solventsystem. For example, an illustrative ink may include both capped silverparticles and capped gold particles each suspended in a suitable solventsystem.

In certain examples, the metal or metal salt may be dissolved in one ormore of the solvent systems to provide a clear, but not necessarilycolorless, solution. For example, a suitable amount of metal or metalsalt may be added to a solvent or a solvent system such that when themetal or metal salt goes into solution, the overall solution is clear.The overall solution may be colored or may be colorless. In certainexamples, the combination of solvents provides a single phase. Toachieve a single phase when using a solvent system, the amounts of eachsolvent may be adjusted such that a single phase results when thesolvents are mixed. Should more than one phase be present upon mixing,the relative amounts of one or more of the solvents can be altered,e.g., increased or decreased, until a single phase is observed.Alternatively, a third solvent may be added to increase the miscibilityof the first and second solvent.

In accordance with certain examples, the particles may also be producedby adding a capping agent to the metal salt dissolved in the solvent orsolvent system. The capping agent may be effective to isolate theparticle and limit the size of its growth. In certain examples, thecapping agent is a high molecular weight capping agent, e.g., has amolecular weight of at least about 100 g/mole. Illustrative cappingagents include, but are not limited to, organic amines having about 12or more carbon atoms. In certain examples, the organic amine has atleast about 16 carbon atoms, e.g., hexadecylarnine. The organic moietyof the amine may be saturated or unsaturated and may optionally includeother functionalities such as, for example, thiols, carboxylic acids,polymers, and amides. Another group of illustrative capping agentssuitable for use in the methods disclosed herein are thiols having about12 or more carbon atoms. In certain examples, the thiol has at leastabout 6 carbon atoms. The organic moiety of the thiol may be saturatedor unsaturated and may optionally include other functionalities such as,for example, pyrrole and the like. Another group of capping agentssuitable for use are pyridine based capping agent such as, for example,triazolopyridine, terpyridine and the like. Additional suitable cappingagents will be readily selected by the person of ordinary skill in theart, given the benefit of this disclosure.

In certain examples where a capping agent is used, the capping agent maybe dissolved in a suitable solvent or solvent system prior to additionto the metal solution. For example, the capping agent may be dissolvedin a solvent and the solution can be mixed with the metal solution. Inother examples, the capping agent may be added as a solid or liquiddirectly to the metal solution without prior dissolution in a solvent.The capping agent may be added, for example, in incremental steps or maybe added in a single step.

In accordance with certain examples, the amount of capping agent addedto the metal solution may vary depending on the desired properties ofthe resulting capped particles. In some examples, a suitable amount ofcapping agent is added to provide at least about 2% by weight cappingagent in the capped particles. It will be recognized by the person ofordinary skill in the art, given the benefit of this disclosure, that itmay be desirable to use more or less capping agent depending on thedesired properties of the particles and/or the desired properties of theink. For example, to increase the conductivity of particles disposed ona substrate, e.g., a printed wiring board, it may be desirable to adjustthe amount of capping agent until the conductivity is optimized or fallswithin a desired range. It will be within the ability of the person ofordinary skill in the art, given the benefit of this disclosure, toselect suitable amounts of capping agent.

In certain examples, when a capping agent (or a capping agent solution)and the metal salt solution are mixed, a single phase results orremains. In an alternative embodiment, the metal salt solution may be asingle phase prior to addition of the capping agent or capping agentsolution, and, upon addition of the capping agent or capping agentsolution a single phase remains. Additional embodiments where a metalsolution and a capping agent are mixed to provide a single phase will bereadily selected by the person of ordinary skill in the art, given thebenefit of this disclosure.

In certain examples, the capping agent and the metal solution may bemixed using conventional techniques such as stirring, sonication,agitation, vibration, shaking or the like. In some examples, the cappingagent is added to the metal solution while the metal solution is beingstirred. In certain examples, the mixture of capping agent and metalsolution may be stirred until a clear and/or colorless single phasesolution results.

In accordance with certain examples, the particles may also be producedby adding a reducing agent to the metal-capping agent solution. Suitablereducing agents include agents that can convert the metal ions dissolvedin the solution to metal particles that, under selected conditions, willprecipitate out of solution. Illustrative reducing agents include, butare not limited to, sodium borohydride, lithium aluminum hydride, sodiumcyanoborohydride, potassium borohydride, sodium triacetoxyborohydride,sodium diethyldihydridoaluminate, sodium tri- ortert-butoxohydridoaluminate, sodium bis(2-methoxyethoxo)dihydridoaluminate, lithium hydride, calcium hydride, titanium hydride,zirconium hydride, diisobutylaluminum dydride (DIBAL-H), dimethylsulfideborane, ferrous ion, formaldehyde, formic acid, hydrazines, hydrogengas, isopropanol, phenylsilane, polymethylhydrosiloxane, potassiumferricyanide, silanes, sodium hydrosulfite, sodium amalgam, sodium(solid), potassium (solid), sodium dithionite, stannous ion, sulfitecompounds, tin hydrides, triphenylphosphine and zinc-mercury amalgam.The exact amount of reducing agent added to the metal-capping agentsolution may vary, but typically the reducing agent is added in excesssuch that substantially all of the dissolved metal is converted from acharged state to an uncharged state, e.g., Ag⁺¹ is converted to Ag⁰.

In some examples, the reducing agent is dissolved in a solvent prior toaddition to the metal-capping agent solution, whereas in other examples,the reducing agent is added to the metal-capping agent solution withoutprior dissolution. When a solvent is used to dissolve the reducingagent, the solvent is preferably non-reactive such that the solvent isnot altered or changed by the reducing agent. Illustrative solvents foruse with the reducing agent include, but are not limited to,tetrahydrofuran (THF), N,N-dimethylformamide (DMF), ethanol, toluene,heptane, octane and solvents having six or more carbon atoms. The personof ordinary skill in the art, given the benefit of this disclosure, willbe able to select suitable solvent for dissolving the reducing agent.

In accordance with certain examples, the reducing agent and cappingagent-metal solution may be mixed or stirred for a sufficient time topermit reaction of the reducing agent with the metal. In some examples,the stirring may be performed at room temperature, whereas in otherexamples the stirring or mixing is performed at an elevated temperature,e.g., about 30° C. to about 70° C., to speed the reduction process. Whenan elevated temperature is used, it is desirable to keep the temperaturebelow the boiling point of the solvent or solvent system to reduce thelikelihood of solvent evaporation, though in some examples, it may bedesirable to reduce the overall volume of solvent.

In accordance with certain examples, the particles may also be producedby isolating the capped metal particles from the single phase solution.Isolation may occur, for example, by decanting, centrifugation,filtering, screening or addition of another liquid that the capped metalparticles are insoluble in, e.g., extraction. For example, a liquid,such as methanol, acetone, water or a polar liquid, may be added to anorganic solution obtained from adding metal salt, capping agent andreducing agent to an organic solvent or organic solvent system. Incertain examples, multiple, separate additions of the extraction liquidmay be added to the solution to remove the capped metal particles. Forexample, a first amount of extraction liquid may be added to remove someof the metal particles. This first amount of extraction liquid may thenbe removed, decanted or otherwise separated from the organic solution,and additional amounts of the extraction liquid may be added to theorganic solution. The exact amount of extraction liquid used to isolatethe metal particles may vary depending on the volume of solvent used toproduce the capped metal particles. In some examples, about two to fourtimes or more solvent is used to extract the capped metal particles,e.g., if the metal particles are produced in about five Liters ofsolvent, then about 20 Liters or more of extraction liquid may be used.It will be within the ability of the person of ordinary skill in theart, given the benefit of this disclosure, to select suitable solventsand amounts of suitable solvents.

In accordance with certain examples, the capped particles may beseparated from the extraction liquid using conventional techniques suchas decanting, centrifugation, filtration and the like. In some examples,the extraction liquid may be evaporated leaving the capped particles.The capped particles may be washed, sized, heated or otherwise processedprior to, during or after separation from the extraction liquid. Incertain embodiments, the extraction liquid may be used, optionally alongwith one or more solvents, as a carrier fluid to provide an ink, asdiscussed in more detail herein.

In accordance with certain examples, the capped particles may be driedto remove any residual liquids. For example, the capped particles may bedried in an oven, may be dried using a vacuum, or may be subjected tolyophilization to otherwise remove any residual extraction liquid and/orsolvent. The dried, capped particles may be stored at room temperatureoptionally in a sealed container to prevent moisture entry.

In accordance with certain examples, the capped particles may beprocessed to remove the capping agent prior to use of the particles inan ink. The capping agent typically remains on the surface of theparticles after the reaction, but the presence of a capping agent may beundesirable. For example, where it is desirable to use particles withthe lowest level of organic contamination possible, it would beadvantageous to remove the capping agent from the capped particles. Incertain embodiments, the capped particles may be processed until thelevel of capping agent is reduced below about 2% by weight, moreparticularly reduced to below about 1% by weight, e.g., the cappingagent is present at less than 0.5% or 0.1% by weight.

In accordance with certain examples, the particles disclosed herein maybe used to provide alloys. In certain examples, the capped particlesdisclosed herein may be used to provide a core-shell structure where themetal of the capped particle acts as a shell and another metal or metalalloy would act as a core. For example, a tin-copper alloy may be usedas a core and silver particles (capped or uncapped) may be used as ashell to provide a type of SAC alloy, e.g., a nano SAC alloy. The exactprocess used to produce the alloy may vary, and in certain examples thealloy may be produced by dissolving ions of other metals, e.g., Sn²⁺,Cu²⁺, etc., in a dispersion of uncapped silver particles. The mixturemay be subjected to reduction or other steps to produce an alloy havingselected properties. In certain examples, the alloys may be placed in asuitable solvent system to provide an ink suitable for use in printingapplications, e.g., inkjet printing applications.

In accordance with certain examples, the produced particles may bedissolved in a solvent system to provide selected properties, e.g., asuitable viscosity and surface tension, such that the particles may beprinted onto a substrate using inkjet printing. In certain examples, aselected amount of particles are dispersed in a carrier to provide anink. The exact amount of the particles selected may vary, and typicallya suitable amount of particles (either capped or uncapped) are used toprovide a dispersion including about 5 weight percent particles to about60 weight percent particles, more particularly about 5-30 weight percentparticles, e.g., about 20-25 weight percent particles. In embodimentswhere capped particles are used, the amount of the capped particles usedmay be altered to account for the additional weight added by the cappingagent. In other examples, a sufficient amount of particles are used toprovide a desired viscosity for the dispersion. For example, theviscosity of the dispersion may vary depending on the method or devicesthat the ink is to be used in. In examples where the ink is intended tobe used in spin coating applications, a sufficient amount of particlesmay be selected to provide an ink viscosity of about 0.25 cPs to about 2cPs, more particularly about 0.5 cPs to about 1.5 cPs, e.g., about 1cPs. In examples where the ink is intended to be used in inkjet printingapplications, a sufficient amount of particles may be selected toprovide an ink viscosity of about 5 cPs to about 20 cPs, moreparticularly about 7 cPs to about 15 cPs, e.g., about 8-10 or 8-9 cPs.Similarly, where the ink is intended to be used in spin coatingapplications, a sufficient amount of particles may be selected toprovide a surface tension of about 18 dynes/cm to about 32 dynes/cm,more particularly about 20 dynes/cm to about 28 dynes/cm, e.g., about 24dynes/cm. In examples where the ink is intended to be used in inkjetprinting applications, a sufficient amount of particles may be selectedto provide an ink viscosity of about 4 cPs to about 50 cPs, moreparticularly about 8 cPs to about 15 cPs, e.g., about 10 cPs. It will bewithin the ability of the person of ordinary skill in the art, given thebenefit of this disclosure, to select suitable solvent systems forimparting a desired property to an ink.

In accordance with certain examples, the carrier of the ink may be oneor more of the solvent systems disclosed herein that can effectivelydisperse the particles in a selected manner, e.g., spin coating, inkjetprinting, paste printing, etc. In certain examples, the carrier is asolvent system that includes a first component and a second component.In certain examples, the dielectric constant of the first component isless than that of the second component. In some examples, the firstcomponent is substantially non-polar with a dielectric constant at 20°C. that is less than about 4, more particularly less than about 3 orless than about 2. In certain examples, the second component has adielectric constant that is preferably greater than about 2, morepreferably greater than about 3 or about 4, provided that the dielectricconstant of the second component is typically greater than that of thefirst component.

In certain examples, the first component may be selected to provide fordispersion of the particles. The second component may be selected toprovide the ability to adjust the viscosity and surface tension of thedispersion. Viscosity modifiers that dissolve in one or both of thefirst component and the second component may also be used. For example,typical viscosity modifiers that may be used include, but are notlimited to, ethylene glycol, propylene glycol or other polyols. Uponheating, glycols should easily decompose and evaporate withoutcompromising conductivity of the final product.

In accordance with certain examples, the solvent system may include atleast two solvents with one solvent being a substantially non-polarmolecule, e.g., a hydrocarbon, and the second solvent being a solventthat is more polar than the first solvent. In examples where ahydrocarbon solvent is used, the hydrocarbon may be saturated orunsaturated, may be straight-chain, branched, cyclic or take otherforms. The solvent may also be a substituted hydrocarbon, e.g., ahalocarbon, or may be an ether (either linear or cyclic), a furan orother substituted hydrocarbon that is substantially non-polar. In someexamples, the substantially non-polar molecule of the first solvent maybe benzene, toluene, xylene, mesitylene or a cyclic hydrocarbon that mayinclude, for example, one or more phenyl groups or saturated orunsaturated cyclic hydrocarbons. Additional solvents for use as thefirst component of the solvent systems disclosed herein will be readilyselected by the person of ordinary skill in the art, given the benefitof this disclosure.

In accordance with certain examples, the solvent system may also includea second component that is more polar than the first component. Thesecond component may be a solvent that includes at least one hydroxyl,amino, sulfo, nitrile, carboxy or other group. In some examples, thesecond solvent may be an alcohol such as, for example, methanol,ethanol, 2-methoxyethanol, propanol, isopropanol, butanol, 2-butanol,pentanol, hexanol, heptanol, octanol or terpeniol. In other examples,the second solvent may include a cyclic alcohol, such as cyclohexanol.In some examples, the second solvent may be a ketone such as, forexample, acetone, methylethylketone, methylisoamylketone, ormethylisobutylketone. In yet other examples, the second solvent mayinclude an amine, amide group or carboxyl group optionally with one ormore hydroxyl groups. In additional examples, the second solvent mayinclude one or more —SH groups optionally with one or more hydroxylgroups. In certain examples, the second solvent may bedimethylformamide, dimethylsulfoxide, N,N-dimethylacetamide, ethylacetate, N-methyl-2-pyrrolidone, pyridine, tetramethyl urea, acetic acidor water. Additional solvents for use as the second component of thesolvent systems disclosed herein will be readily selected by the personof ordinary skill in the art, given the benefit of this disclosure.

In certain examples, the solvent system may include a mixture of thefirst component and the second component at any desired ratio. Incertain examples, the amounts of the first component and the secondcomponent that are used are selected to provide an ink viscosity ofabout 10-12 cPs at a printing temperature. In other examples, theamounts of the first component and the second component that are usedare selected to provide an ink having a surface tension of about 30-32dynes/cm. Illustrative ratios of first component:second component are4:1, 3:1, 2:1, 1:1, 1:2, 1:3, 1:4, and any ratio in between theseratios.

In accordance with certain examples, the solvent system may includethree or more solvents. The exact ratio of the solvents used typicallydepends on the desired properties of the ink. In certain configurations,the ratios of the solvent are selected to provide an ink that isamenable to disposition using inkjet printing applications. In someexamples, the ratios of the solvents are selected to provide a viscosityof about 10-12 cPs and/or a surface tension of about 30-32 dynes/cm. Itwill be within the ability of the person of ordinary skill in the art,given the benefit of this disclosure, to select suitable ratios ofsolvents for use in a solvent system that includes three or moresolvents.

In accordance with certain embodiments, a solvent system may be selectedsuch that an ink used to produce a high-aspect ratio conductive patternhas a viscosity of about 10-12 cPs at a printing temperature. Inks thatinclude a viscosity of about 10-12 cPs are especially useful in inkjetprinting applications, such as those using, for example, piezoelectricprinting heads from Spectra or Xaar. In some examples, the ink mayinclude capped metal particles suspended in a suitable solvent system,e.g., a mixture of toluene, terpeniol and optionally xylene, to providea viscosity of about 10-12 cPs. In certain examples, the ink may includecapped silver particles, capped gold particles, or mixtures thereof.

In accordance with certain examples, a solvent system may be selectedsuch that an ink used to produce a high-aspect ratio conductive patternhas a surface tension of about 30-32 dynes/cm at a printing temperature.Inks that include a surface tension of about 30-32 dynes/cm areespecially useful in inkjet printing applications, such as those using,for example, piezoelectric printing heads from Spectra or Xaar. In someexamples, the ink may include capped metal particles suspended in asuitable solvent system, e.g., a mixture of toluene, terpeniol andoptionally xylene, to provide a surface tension of about 30-32 dynes/cm.In certain examples, the ink may include capped silver particles, cappedgold particles, or mixtures thereof.

In accordance with certain examples, the inks disclosed herein may haveboth a viscosity of about 10-12 cPs and a surface tension of about 30-32dynes/cm. To achieve both properties, the relative amounts of thecomponents in the solvent system may be adjusted. In addition, more orless capped metal particles may be used to achieve a desired viscosityand a desired surface tension for the ink. The person of ordinary skillin the art, given the benefit of this disclosure, will be able to adjustthe amounts of capped metal particles and the components in a solventsystem to achieve desired physical properties.

In accordance with certain examples, an ink that is finely dispersed andstable at a printing temperature may be used to produce a high-aspectratio conductive pattern. In certain examples, stability may be assessedby determining whether or not the capped metal particles precipitate outof solution. It is desired that the capped metal particles be suspendedin the solvent system to facilitate transfer of the capped metalparticles to a substrate during printing. Substantial precipitation ofthe capped metal particles may result in poor transfer of material fromthe printer to the substrate. To increase stability of the ink, one ormore dispersants may be added to the ink. Illustrative dispersantsinclude, but are not limited to, Solsperse 17000, 20000 and 39000 fromNoveox Corp or Disperbyk 112, 117, 1250 from BYK.

In accordance with certain examples, the ink may be processed prior touse. In certain embodiments, the ink may be mixed with dyes, other inksor other materials prior to use. In other embodiments, the ink may beheated, screened, filtered or the like prior to use. In certainexamples, the particles may be heated, screened, filtered or the likeprior to disposition in a solvent system to provide an ink. In certainembodiments employing the capped particles disclosed herein, heatingpermits the particles to coalesce and form highly conductive lines orpatterns that may be used, for example, in circuits, printed wiringboards and the like. Additional embodiments for disposing inks on asubstrate to create a desired pattern will be readily selected by theperson of ordinary skill in the art, given the benefit of thisdisclosure. Illustrative uses for articles produced using the inksdisclosed herein include, but are not limited to, printed electricalcircuits, radio frequency identification (RFID) antennas, solar cellwires, solar cell interconnect, battery electrodes, and reflectivesurfaces and mirrors.

In accordance with certain examples, the type and nature of thesubstrate depends, at least in part, on the desired device that is to beproduced. For example, in application where a printed circuit board isproduced, the substrate may be one or more cured or uncured prepregs.The substrates may be made from may different materials, including butnot limited to, traditional silicon and also polymeric substrates suchas for example, polyethylene, polypropylene, polyimide and polyester.These substrates are relatively inexpensive to make and provide goodadhesion of electronic components. The substrate may include reinforcingfibers or whiskers, may include glasses, additives, foams, flameretardants and other materials to impart desired properties to thesubstrate.

In embodiments where an ink is subjected to heating, heating istypically performed using a hot-plate, oven (high temperature convectionoven, reflow oven, IR oven, etc.), laser heating or other methods anddevices that can increase the temperature of the particle dispersion orthe ink. In certain examples, the ink may be heated to at least about250° C. for 10-60 seconds, e.g., 250° C. for 30 seconds. In otherexamples, sequential heating may be performed such that the ink isheated at a first temperature for a selected time followed by heating ata second temperature for a selected time. For example, the ink may beheated at about 110-130° C. for 10-30 seconds, e.g., 120° C. for 20seconds, followed by a second heating step at 250-300° C. for 10-60seconds, e.g., 280° C. for 20 seconds. Subsequent to heating, theparticles and inks may be subjected to other processing steps.

In accordance with certain examples, the inks disclosed herein may beused along with a suitable apparatus for disposal of the inks. While theexact method used to dispose the ink on a substrate is not critical, anon-impact printing device, such as, for example, an inkjet printer, maybe used to print the ink onto a substrate. In embodiments where aninkjet printer is used, the inkjet printer includes an ink reservoir orcartridge that holds the ink. The ink cartridge is in fluidcommunication with a print head, which typically includes a series ofnozzles that spray the ink onto the substrate. The inkjet printer mayalso include a suitable motor to move the print head to a desiredposition. One or more belts or chains may connect the motor to the printhead. The inkjet printer may include stabilizer bars or supports tostabilize the print heat during the printing process. Illustrativeinkjet printers suitable for use include, but are not limited to, thoseusing or configured to use piezoelectric printing heads from Spectra orXaar. Other suitable inkjet printers will be readily selected by theperson of ordinary skill in the art, given the benefit of thisdisclosure.

In certain embodiments, one or more devices that includes at least oneconductive line or pattern produced using the methods disclosed hereinis provided. In certain examples, the device may be a conducting grid ona solar cell, a plasma display, a printed circuit board, a solar cellinterconnect, an electronic circuit or other devices that could benefitfrom highly defined conductive lines or patterns.

In accordance with certain examples, a printed circuit board comprisinga dielectric substrate and having at least one high-aspect ratioconductive pattern disposed on the dielectric substrate is disclosed. Incertain examples, a printed circuit board comprises a dielectricsubstrate having an electrical conductor, e.g., a wiring layer, on oneor both surfaces. Any portion or portions of the conductor may include ahigh-aspect ratio conductive pattern. In certain examples, theelectrical conductor may be formed to have a predetermined pattern, withsome portion, or all, of the electrical conductor being formed using themethods disclosed herein. In examples employing multiple electricalconductors, the conductors may be connected electrically with eachother. In some examples, the dielectric substrate comprises a glasscloth or a glass non-woven fabric such as, for example, the illustrativeglass cloths and glass non-woven fabrics discussed herein.

In accordance with certain examples, a high-aspect ratio conductivepattern disclosed herein may be disposed on one or more prepregs. Aprepreg typically includes a substrate (e.g., woven or non-woven fibroussubstrate) such as glass, quartz, polyester, polyamide, polypropylene,cellulose, nylon or acrylic fibers, low dielectric unidirectional tape,or woven cloth or non-woven fabric of interbonding fibers. Suitable lowdielectric fibers include high strength fibers such as glass fibers,ceramic fibers and aramid fibers, which are commercially available. Incertain examples, prepreg fibers may have a consistent fiberorientation. The prepreg may be impregnated with a composition, such asa flame retardant, and such prepregs may be cured by application of heatand pressure. The prepreg may be cured prior to disposition of ahigh-ratio conductive pattern, or may be disposed subsequent to thedisposition of a high-ratio conductive pattern. In certain instances, itmay be desirable to not cure the prepreg. Referring now to FIG. 5,prepreg 500 comprises a generally planar substrate 510 with ahigh-aspect ratio conductive pattern 520 disposed on or in substrate510. In FIG. 5, the high-aspect ratio conductive pattern 520 is shown asa line, though as discussed herein, other shapes and configurations maybe achieved, such as a semi-circular high-aspect ratio conductivepattern 530. The thickness of the substrate 510 can vary, and in certainexamples, the substrate is about 1 mil to about 15 mils thick, moreparticularly, about 1 mil to about 10 mils thick, e.g., about 2-9, 3-8,4-7 or 5-6 mils thick. It will be within the ability of the person ofordinary skill in the art, given the benefit of this disclosure, toselect suitable thicknesses for prepreg substrates.

In accordance with certain examples, the conductive patterns 520 and 530may be disposed on the substrate 510 using any of the methods disclosedherein. In certain examples, the conductive patterns may be disposedusing inkjet printing or other suitable devices and methods.

In accordance with certain examples, a printed circuit board comprisingone or more of the compositions disclosed herein is provided. Examplesof printed circuit boards include a dielectric substrate having anelectrically conductive layer, e.g., a wiring layer, on one or moresurfaces. In some examples, the electrically conductive layer is formedto have a predetermined pattern. In examples using multiple electricallyconductive layers, the layers may be connected electrically with eachother. The exact nature of the dielectric substrate can vary, andexemplary materials for dielectric substrates include but are notlimited to glass, woven and non-woven fabrics, and other suitablematerials that can receive one or more of the compositions disclosedherein.

Several specific examples are disclosed below to facilitate a betterunderstanding of the technology described herein. In all the examplesdisclosed below, unless otherwise noted, all formulations were ballmilled for 48 hours and provided a stable dispersion of particles forweeks without visible precipitation.

Example 1

A batch of silver particles was prepared by adding 108 grams of silvernitrate to 200 millimeters (mL) of ethylene glycol to provide a silvernitrate concentration of 3.2 moles/Liter. The entire 200 mL solution wasadded to 1500 mL of ethanol to which 2750 mL toluene was added in orderto obtain a single phase mixture (provided a 1:1.83 mixture ofethanol:toluene).

In a first reaction, 318.7 grams of hexadecylamine was added to thesingle phase mixture, and a single phase remained after stirring. Tothis clear solution, 250 mL of a sodium borohydride solution inN,N-Dimethyl formamide (11.349 grams of sodium borohydride dissolved in250 mL of N,N-Dimethyl formamide) was added drop-wise as a reducingagent to form a dark yellowish brown solution of about 4.7 liters involume. The reaction mixture was allowed to stir for 30 minutes at about22° C., and capped silver particles were extracted by adding 20 L ofmethanol or 20 L of acetone. The capped particles were removed byseparatory funnel followed by centrifugation at 500 rpm for 30 minutesusing a Rousselet Robatel® RC 20 centrifuge. The capped particles weredried in a vacuum to obtain a free flowing powder of nanocrystallinecapped silver particles having about 18% hexadecylamine.

In a second reaction, 24 grams of dodecylamine was added to the singlephase mixture and a single phase remained after stirring. To this clearsolution, 250 mL of a sodium borohydride solution in N,N-Dimethylformamide (11.349 grams of sodium borohydride dissolved in 250 mL ofN,N-Dimethyl formamide) was added drop-wise as a reducing agent to forma dark yellowish brown solution of about 4.7 liters in volume. Thereaction mixture was allowed to stir for 30 minutes at about 22° C., andcapped silver particles were extracted by adding 20 L of methanol or 20L of acetone. The capped particles were removed by separatory funnelfollowed by centrifugation at 500 rpm for 30 minutes in a RousseletRobatel® RC 20 centrifuge. The capped particles were dried in a vacuumto obtain a free flowing powder of nanocrystalline capped silverparticles having about 8% dodecylamine.

Each of the capped particle samples was dispersed in toluene, and aclear absorption at 409-416 nm was observed using a Hewlett-Packard®UV-Visible Spectrophotometer (Model No.: HP8452A) and a 1 cm path lengthdisposable cuvette. An absorbance at 409-416 nm absorption is typical ofnanocrystalline silver.

Example 2

Depending on the applications for which the metal particles areintended, different loading rates may be used. The following loadingrates have been used to produce particles. In parenthesis is the liquidused to extract the metal particles from the single phase solution.

Sample Percent Loading (%) Ag-HDA (Methanol ppt) 18.69 Ag-HDA(Acetoneppt) 2.63 Ag-DDA (Methanol ppt) 7.35 Ag-DDA (Acetone ppt) 2.50

Example 3

Capped particles were produced using the protocol described in Example 1and with varying loading rates of hexadecylamine. Particles wereproduced that had 18% by weight hexadecylamine or 8% hexadecylamine. Acommercial powder (70 nm in size) that was commercially available fromSigma-Aldrich and 40 nm powder (type 3) available from an industrialsupplier (Nanodynamics, Inc. of Buffalo, N.Y.) were tested along withthe two particle samples.

FIG. 5 shows thermo-gravimetric analysis of three different thin filmsproduced using the three materials. Type one material was coated with18% HDA, type 2 was coated with 8% HDA and type 3 was the commerciallyavailable powder with 2% of an organic coating. Three different silverinks were made by mixing or dispersing of one of the selected materialsin toluene (about 6% solution by weight). Thin films were made on glassby spin coating the inks at similar conditions. The glass substrateswith wet films were then heated at 200° C. for 100 seconds. Upon heatingHDA and the solvent decomposed and evaporated to provide a surface ofsilver particles. Such particles easily and completely coalesced and theink made of silver particles with 18% of HDA coating produced thinsilvery and shiny films. Both of the inks made of silver nanopowder withonly 8% HDA coating and made of commercially available produced dark andloose grayish films.

The conductivity of the films was measured by conventional 4-point probemeter (Lucas Labs model Pro4). The films made of 18% HDA coatednanopowder produced highly conductive films with the conductivity in therange of 30-40*10⁴ S/cm, which was only slightly lower then theconductivity of the bulk silver (˜62*10⁴ S/cm). The films also have hadvery good adhesion to the glass substrate and easily passed tape andscratch tests usually used to evaluate the adhesion properties (ASTMD3359-02 dated Aug. 10, 2002).

Example 4

Metal particles prepared according to Example 1 above may be dispersedin toluene to provide an ink. In one illustration, metal particles maybe dispersed in toluene to provide 20 weight percent particles and asolution viscosity of about 1 cPs. The ink may be applied to a substrateusing spin coating, for example, or may be used in spin coatingapplications. The particles may be silver or gold particles or otherillustrative metals disclosed herein.

Example 5

Metal particles prepared according to Example 1 above may be dispersedin IsoPar® G solvent to provide an ink. In one illustration, metalparticles may be dispersed in IsoPar® G solvent to provide 20 weightpercent particles and a solution viscosity of about 1 cPs. The ink maybe applied to a substrate using spin coating, for example, or may beused in spin coating applications. The particles may be silver or goldparticles or other illustrative metals disclosed herein.

Example 6

Metal particles prepared according to Example 1 above may be dispersedin an organic solvent mixture to provide an ink. In one illustration,metal particles may be dispersed in toluene/Isopar® L solvent/Isopar® Vsolvent (1:2:8) to provide 20 weight percent particles and a solutionviscosity of about 8-9 cPs. The ink may be applied to a substrate usinginkjet printing devices and methods, for example, or may be used ininkjet applications. The particles may be silver or gold particles orother illustrative metals disclosed herein.

Example 7

Metal particles prepared according to Example 1 above may be dispersedin an organic solvent mixture to provide an ink. In one illustration,metal particles may be dispersed in toluene/Isopar® V solvent (1:2) and3 weight percent polyisobutylene (PIB) to provide 20 weight percentparticles and a solution viscosity of about 8-9 cPs. The ink may beapplied to a substrate using inkjet printing devices and methods, forexample, or may be used in inkjet applications. The particles may besilver or gold particles or other illustrative metals disclosed herein.

Example 8

Metal particles prepared according to Example 1 above may be dispersedin an organic solvent mixture to provide an ink. In one illustration,metal particles may be dispersed in toluene/Isopar® V solvent (1:1) toprovide 80 weight percent particles. The ink may be applied to asubstrate using paste printing methods, for example, or may be used inpast printing applications. The particles may be silver or goldparticles or other illustrative metals disclosed herein.

Example 9

Several inks were prepared by placing capped silver particles intoluene. Each of the capped silver particles used in the inks wasprepared using the protocol of Example 1 and extracted in methanol onceunless otherwise noted. The various inks are shown in the table below.The silver particles in Ink B were washed in methanol twice, and thesilver particles in Ink C were extracted using acetone. Inks F and Gwere made from commercially available silver nanoparticles. Inparticular, Inks F and G were made by dispersion of silver powder intoluene in the weight ratio 1:5. The ink was sonicated for 60 min priorto making the films. Ink F was made from Aldrich powder (Cat#57583-2),and Ink G was made using Nanodynamics Product Name NDSilver (Lot#31-0048).

Ink Capping Agent Amount of Capping Agent (%) Ink A Hexadecylamine 18 Ink B Hexadecylamine 12-14 Ink C Hexadecylamine 2-3 Ink D Dodecylamine 8Ink E Octylamine 5-6 Ink F (Commercial NA 4 Product 1) Ink G (CommercialNA   0.5 Product 2)

Each of the inks was used in a spin coating process to form a film. Toform each film, each ink was heated on a hot plate at 250° C. for 30seconds. After heating, each ink was spin coated onto a glass substrateusing a KW-4A spin coater commercially available from Chemat Technology(Northridge, Calif.). The coating procedure involved coating at 600 rpmfor 9 seconds followed by coating at 1000 rpm for 30 seconds. Theresulting properties of each film are shown below. Adhesion was testedby tape test according to ASTM D3359-02 dated Aug. 10, 2002. Theresistivity of each film was measured using a 4-point probe (LucasLabs).

Ink Film Description Adhesion Resistivity (μΩ × cm) Ink A Shiny, smoothand Very good, passed 3-4 uniform (FIG. 6A). tape test Ink B Shiny,uneven with Good 3-4 pinholes (FIG. 6B) Ink C Did not form a film ∞ InkD Shiny, uneven, Poor 20-30 numerous pinholes (FIG. 6C) Ink E Does notform a ∞ film, crumbles on heating Ink F Does not form a ∞ film, greyagglomerates present Does not form a film

Example 10

A composition was prepared comprising the following materials: asufficient amount of nanosilver capped with hexadecylamine (produced asdescribed above in Example 1) was dispersed in a solvent system thatincluded 1 part toluene, 4 parts terpeniol and 4 parts xylene to provide20 weight percent nanosilver coated with hexadecylamine in thedispersion.

The surface tension and the viscosity of the dispersion were measured.Surface tension was measured using a Capillary Surface Tension Apparatusfrom Fisher. Viscosity was measured using a Brookfield DigitalViscometer DV-11. The surface tension was found to be 30 dynes/cm, andthe viscosity was found to be 10 cPs.

Example 11

A composition was prepared comprising the following materials: asufficient amount of nanosilver capped with hexadecylamine (produced asdescribed in Example 1) was dispersed in a solvent system that included4 parts toluene, 1 part terpeniol, 4 parts xylene and 0.1 g/L ethyleneglycol to provide 20 weight percent nanosilver coated withhexadecylamine in the dispersion.

The surface tension and the viscosity of the dispersion were measured asdescribed in Example 10. The surface tension was found to be 32dynes/cm, and the viscosity was found to be 14 cPs.

Example 12

A composition was prepared comprising the following materials: asufficient amount of nanosilver capped with dodecylamine (produced asdescribed in Example 1) was dispersed in a solvent system that included4 parts butanol and 1 part toluene to provide 20 weight percentnanosilver coated with dodecylamine in the dispersion. The surfacetension and the viscosity of the dispersion were measured as describedin Example 10. The surface tension was found to be 30 dynes/cm, and theviscosity was found to be 10 cPs.

When introducing elements of the examples disclosed herein, the articles“a, “an,” “the” and “said” are intended to mean that there are one ormore of the elements. The terms “comprising,” “including” and “having”are intended to be open-ended and mean that there may be additionalelements other than the listed elements. It will be recognized by theperson of ordinary skill in the art, given the benefit of thisdisclosure, that various components of the examples can be interchangedor substituted with various components in other examples.

Although certain aspects, examples and embodiments have been describedabove, it will be recognized by the person of ordinary skill in the art,given the benefit of this disclosure, that additions, substitutions,modifications, and alterations of the disclosed illustrative aspects,examples and embodiments are possible.

1. A device comprising at least one high-aspect ratio conductivepattern, wherein the device comprises a substrate and wherein the highaspect ratio conductive pattern is produced by: a. disposing a supportlayer on the substrate defining a spacing having an effective height; b.disposing a conductive material between the defined spacing of thesupport layer; and c. removing the support; wherein further supportlayers can be disposed followed by disposing of additional conductivematerial to increase the effective height of the high aspect ratioconductive pattern, prior to removing the support.
 2. (canceled)
 3. Thedevice of claim 1 in which the conductive pattern is a conductive line.4. The device of claim 1 in which the high-aspect ratio conductivepattern comprises metal particles.
 5. The device of claim 4 in which themetal particles are capped metal particles.
 6. The device of claim 5 inwhich the capped metal particles provide a conductivity of at leastabout 30*10⁴ S/cm.
 7. The device of claim 5 in which the capped metalparticles are one or more members selected from the group consisting ofsilver, gold, copper, nickel, platinum, palladium, and iron.
 8. Aprinted circuit board comprising: a substrate; at least one high-aspectratio conductive pattern disposed on the substrate wherein the highaspect ratio conductive pattern is produced by: a. disposing a supportlayer on the substrate defining a spacing having an effective height; b.disposing a conductive material between the defined spacing of thesupport layer; and c. removing the support; wherein further supportlayers can be disposed followed by disposing of additional conductivematerial to increase the effective height of the high aspect ratioconductive pattern, prior to removing the support.
 9. The printedcircuit board of claim 8 further comprising at least one electricalconductor electrically coupled to the high-aspect ratio conductivepattern.
 10. The printed circuit board of claim 8 in which the substrateis one or more prepregs.
 11. The printed circuit board of claim 8 inwhich the high-aspect ratio conductive pattern comprises metalparticles.
 12. The printed circuit board of claim 11 in which the cappedmetal particles provide a conductivity of at least about 30*10⁴ S/cm.13. The printed circuit board of claim 11 in which the capped metalparticles are one or more members selected from the group consisting ofsilver, gold, copper, nickel, platinum, palladium, and iron. 14-25.(canceled)